Change BasemapGallery thumbnail size

I am looking for a way to change the size of the thumbnails within the basemapGallery. I have thumbnails that are 300x200px but the gallery seems to have a default size of around 60x50px which it forces all thumbnails to. i would like to increase the size of these thumbnails but cannot find a single example of how to do this, or any reference anywhere regarding thumbnail size.

I do not think that you can change the size of these thumbnails in Esri's out-of-the-box galleries. You will likely have to custom create your own landing page to make a gallery of maps/apps in order to make the thumbnails different. Though, I could be wrong...